I tried so many ways to delete this duplicate. It is appearing in search results before my main listing. Someone created it ages ago, and now I have access to manage both. I have followed every article on the web but it just won't go away. Getting sick of the wrong phone number from another building on the property being shown. All we do is answer that phone to tell them to call the other phone number.

Because it isn't a 'true' duplicate (it has a different address) you'll need to contact GMB support to have it removed completely as an incorrect page. If you have Twitter contact @GoogleMyBiz and ask them to remove that page as it shows a business that never existed at that address. If you don't have Twitter you can use phone support at this link: https://support.google.com/business/contact/business_c2c_l?rd=3# to request the page be removed entirely.